The invention generally relates to electric incandescent lamps, and more particularly to multiple filament lamps sequentially lightable one at a time by turning.
Multiple filament lamps are well known in the prior art, and fall into two classes: those that do not require the removal of the lamp from the socket to change filament connections, and those that do. In the first category, U.S. Pat. No. 599,910 to J. T. Lister more closely resembles the invention in purpose and result, differing in structure and functioning. It teaches two conductor springs of different lengths, the longer for contacting two terminals and the shorter for contacting only one terminal of the four terminals provided for two filaments. By turning the lamp in its base 180.degree. the longer conductor spring is shifted from one set of filament terminals to the other to light the filament having both its terminasl contacted, the other filament circuit being uncompleted is not energised. The invention teaches a single conductor spring that in cooperation with a common ground energizes four filaments in succession by turning 270.degree. in 90.degree. increments. Also cited is G. Piersimoni, U.S. Pat. No. 1,863,500 that teaches a rotatable ring on a base and a common ground to successively light one of two filaments that are removable from the lamp.
In the second category, U.S. Patents to Dill, 3,886,400; Marinace, 3,673,534; Rohner, et al, 1,449,627; Wide, 1,445,120; and Ball, 476,183, generally provide selectors that have to be rotated or removed to successively energize filaments of a multiple filament lamp and/or couple them for increased light. In all cases this defeats the main purpose of the invention which is to reduce the number of times a maintenance man has to remove lamps from sockets in a building where a large number are kept burning over long periods of time.